The average time spent playing games rose year-on-year in the U.S., research firm NPD Group said Thursday.

U.S. gamers ages 2 and up spend 13 hours per week playing games, according to a summary of the firm's Gamer Segmentation 2010 report. That's up from 12.3 hours per week in 2009.

The players that log the most hours -- a category NPD dubbed "extreme gamers" -- averages 48.5 hours per week, or over two days of gaming. Extreme gamers make up just 4 percent of the market, NPD said.

Overall, the number of hours spent playing console games per week grew 9 percent, and the time spent playing PC games rose 6 percent. Portable gaming hours fell 16 percent among U.S. gamers.

Gamers' average age increased slightly from 2009 as well, up to 32 from 31 years of age. "Avid" PC gamers and offline PC gamers are the segments with the oldest players, with gamers averaging 42 years old in both categories.

NPD didn't provide hard sales figures, but said that 17 percent of games were purchased digitally, according to the survey, up from 16 percent in 2009. Avid PC gamers are the most frequent downloaders, with 30 percent of their games in the past three months being purchased digitally.

Gamers are also buying and receiving games more frequently, with the number of console and portable games acquired rising 16 percent and 10 percent, respectively.

NPD said it polled 18,872 members of a consumer panel through an online survey in January this year to collect the data for the report.